SYSTEMATICS The study of biological diversity in an evolutionary context encompasses both taxonomy and phylogeny

Taxonomy Two main objectives: –to sort out organisms into species –to classify species into higher taxonomic levels Species that appear to be closely related are grouped into the same genus. the leopard, Panthera pardus, belongs to a genus that includes the African lion (Panthera leo) and the tiger (Panthera tigris). Taxon = a named taxonomic unit at any level; (taxa = plural) –ex: Mammalia is a taxon at the Class level

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TAXONOMY taxonomic system developed by Linnaeus in the 18th century –binomial = Genus species –classification system Domain Eukarya KingdomAnimalia PhylumChordata ClassMammalia OrderPrimates FamilyHominidae GenusHomo speciessapiens

5 Limitations of the Linnean System Many hierarchies are being re-examined based on the results of molecular analysis -Linnaean taxonomy does not take into account evolutionary relationships -The phylogenetic and systematic revolution is underway

PHYLOGENY Hypothesis of the evolutionary history of a group represented by pictures: phylogenetic trees –time goes from the bottom up –read from bottom up, NOT LEFT TO RIGHT –branch “length” = the number of changes

10 Phylogenies depict evolutionary relationships

Phylogenetic trees reflect the hierarchical classification of taxonomic groups nested within more inclusive groups. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 25.8

Approaches to Constructing Phylogenies Cladistics –uses shared derived characteristics (synapomorphies) to classify organisms –Not shared ancestral characteristics, not overall similarity Because evolution is not steady paced, not unidirectional, may be convergent

14 Examples of ancestral versus derived characters Presence of hair is a shared derived feature of mammals Presence of lungs in mammals is an ancestral feature; also present in amphibians and reptiles Cladistics

17 A Cladogram; DNA Cladistics

18 A Cladogram: DNA Cladistics

Approaches to Constructing Phylogenies Traditional approaches –Used overall similarities –Characters are weighted by the taxonomist

PHYLOGENY systematists prefer monophyletic taxa –a single ancestor gave rise to all species in that taxon and to no species in any other taxa

23 Monophyletic Group Systematics and Classification

24 Paraphyletic Group Systematics and Classification

25 Polyphyletic Group Systematics and Classification

26 Old plant classification system Systematics and Classification

27 New plant classification system Systematics and Classification

Evidence used to reconstruct phylogenies Comparative anatomy, morphology, embryology, etc. –problems of homology vs homoplasy (analogy) homology = likeness due to common ancestry homoplasy or analogy = likeness due to convergent evolution

32 Distribution of saber-toothed mammals Comparative Biology

34 A Cladogram: DNA Can Have Homoplastic Molecular Data

Evidence used to reconstruct phylogenies Protein comparisons DNA comparisons –DNA-DNA hybridization, restriction mapping, DNA sequencing

Character Mapping Once you have a phylogeny you can trace the evolution of characters or traits in that group use the rules of parsimony –the simplest is the best

39 Parsimony and Homoplasy

Phylogenetic Trees are Hypotheses

41 Grouping Organisms Carl Woese proposed a six-kingdom system Prokaryotes Eukaryotes

KINGDOMS Monera = Archaebacteria & Eubacteria –prokaryotic Protista –eukaryotic Plantae –eukaryotic, multicellular, autotrophic, cell walls Fungi –eukaryotic, multicellular, heterotrophic, cell walls Animalia –eukaryotic, multicellular, heterotrophic, no cell walls

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